Cranial Nerves PDF

Arthur Grisha C. Rivera 1-E Cranial Nerves 1. List of cranial nerves and their function: a. Olfactory nerve CN 1 - transmit olfactory signal to brain and responsible for the sense of smell b. Optic nerve CN 2 - responsible for the sense of sight and transmission of visual info...

Arthur Grisha C. Rivera 1-E Cranial Nerves 1. List of cranial nerves and their function: a. Olfactory nerve CN 1 - transmit olfactory signal to brain and responsible for the sense of smell b. Optic nerve CN 2 - responsible for the sense of sight and transmission of visual information from retina to the brain c. Oculomotor nerve CN 3 - it is responsible for the movement of the eye muscle specifically superior rectus, inferior rectus, medial rectus, inferior oblique muscles and levator palpebrae superioris muscle which is for the eyelids d. Trochlear nerve CN 4 - it controls the superior oblique muscle which is responsible for downward and inward eye movement e. Trigeminal nerve CN 5 - Trigeminal has 3 divisions, the ophthalmic and maxillary division is responsible for the sensation in the forehead, cornea and scalp while maxillary is for the sensation of the upper jaw namely the lips, cheek, middle portion of the lips. The mandibular nerve on the other hand is mixed since it controls the muscle of the chewing and sensation of the lower lips, jaw and teeth f. Abducens nerve CN 6 - It is responsible in the outward movement of the eye by controlling the lateral rectus muscle g. Facial nerve CN 7 - It has mixed function since it is a mixed sensory and motor nerve. For sensory nerves it transmits a taste sensation from the anterior ⅔ of the tongue. While the motor is that it controls the facial expressions, including smiling, pounting, and closing of the eye h. Vestibulocochlear nerve CN 8 - it has 2 main components namely vestibular and cochlear nerve. Vestibular is the one that is responsible or the balance and spatial orientation while cochlear is for hearing or auditory information i. Glossopharyngeal nerve CN 9 - is also mixed. It gets sensory information from the posterior ⅓ of the tongue, sensory info from tonsils and pharynx. In terms of their motor function, it controls for stylopharyngeus j. Vagus nerve CN 10 - it controls the organs of the abdomen since it is the longest cranial nerve. It controls muscle in the pharynx, larynx and vocalization. It also provides sensory information in the pharynx, larynx, and internal organs. k. Accessory nerve CN 11 - controls the sternocleidomastoid and trapezius muscles for shoulder and neck movement l. Hypoglossal nerve CN 12 - it is responsible in muscle tongue movement, speech, chewing and swallowing 2. Cranial Nerve Pathways A. Olfactory nerve pathway a. Olfactory receptors - these olfactory receptors are located in the epithelium. These are located in nasal epithelium and are very sensitive in odor.  b. Olfactory nerve filaments - which compact together to form olfactory nerves. These tiny nerve passes through the cribriform plate to reach the olfactory bulb c. Olfactory bulb - is the one that enters into the brain. It is small, round and located in the underside of the frontal bone. d. Olfactory tract - The nerve fibers that extend their axon of the olfactory bulb combine together forming olfactory tract reaching to the different organs of the brain. e. Primary olfactory cortex - The olfactory tracts goes to the temporal lobe which is part of the brain that process the information of the olfaction. f. Other brain area - the olfactory tract also connects to the other area of the brain specifically the limbic parts like amygdala, hippocampus and also hypothalamus responsible for emotion, memory and hormone regulation B. Optic Nerve Pathway - Function - Structures Involved in the Pathway - The pathway is involved in the visual information transmission from retina to the brain. As a result the person will have a visual the ability to perceive and interpret the world around him. a. Retina - it is part of the of the eye in the back that had lots of photoreceptor like rods and cones that converts light into electrical signal b. Optic Nerve - It is the one that exits from the optic canal because it will transmit electrical information from the retina. It is composed of axons c. Optic Chiasm - It is a converging place for the optic nerve seen in the hypothalamus. The only thing that passes and goes to the contralateral side. On the other hand, the temporal nerves do not cross the chism. The optic chiasm ensure that opposite side receive info d. Optic Tract - Once it passes the optic chiasm it will become optic tract leading to lateral geniculate nucleus e. Lateral Geniculate Nucleus - it serve a termination point of the optic tract and processing occurs o the visual signals f. Optic Radiation - It sends the processed signal to the Visual cortex. The location of it is in the occipital lobe. g. Visual Cortex - This is where the interpretation of the color, form, and movement occurs. It also serves a primary area for the processing of visual information. C. Identification of the Visual Pathway 1. Optic nerve 2. Optic Chiasm 3. Optic Tract 4. Lateral Geniculate Nucleus 5. Optic radiation 6. Visual Cortex 3. Exit Points 1. Optic canal - Optic nerve - it is located in the sphenoid bone and also a passageway of ophthalmic artery. Optic nerve is important in the transmission of visual information while the opthalmic artery supplies blood in the eye. If optic nerve is damaged here, there can be vision loss, pain and double vision. Fractures can lead to visual loss. 2. Superior Orbital Fissure - Oculomotor nerve, abducens nerve, trochlear nerve, opthalmic nerve v. 1 - Many cranial nerves pass here lik oculomotor nerve which is responsible for lens accommodation, pupil size and eye movement. Trochlear is responsible for superior oblique muscle and downward inward eye movement. Abducens which control the lateral rectus and are responsible for the downward and inward eye movement. An opthalmic nerve which is responsible for sensation for the cornea, scalp and face. This is a strategic exit since it is near the muscle of the eye and eyelid, and the eye and optic nerve is also near. Clinical significance of this include the possible Superior Orbital Fissure Syndrome that leads to double vision, eye pain, ptosis or drooping of eyelids. 3. Foramen Rotundum - Maxillary nerve V2 - It serves as a passageway of the Maxillary nerve providing sensation in the middle portion of the phase. It also allows for the maxillary nerve to exit the skull and enter the orbit. It divides into several branches of the face. Foramen rotundum is located in the greater wing of the sphenoid bone. If the foramen rotundum is damaged, there will be a facial pain or trigeminal neuralgia. Tumors in the sphenoid bone can lead to facial numbness, pain and vision problem 4. Foramen Ovale - Mandibular nerve V3, lesser petrosal nerve - It serves as a passageway of mandibular nerve, one of the divisions of trigeminal nerve. This is a strategic place since is is near the lower jaw, teeth and lower lips which are all controlled by the mandibular nerve. A place for both sensory and motor innervation. Compression of the nerve in this area will lead to facial pain, numbness and since it has motor innervation, it will be harder to chew also. 5. Internal Acoustic Meatus - Facial nerve, Vestibulocochlear nerve - it is located in the bony canal of temporal bone. This is the passageway facial nerve. This is responsible for controlling facial expression, taste and certain autonomic function. The anterior superior quadrant serves as the location of the internal acoustic meatus. Alongside the acoustic meatus is the vestibulocochlear nerve 6. Jugular Foramen - glossopharyngeal nerve, Vagus nerve, accessory nerve - It is a foramen located in between the occipital and temporal bone. Other than nerves it also serves as passageway of meningeal branches of the internal carotid artery and internal jugular vein. The anterior part is larger and transmits the internal jugular vein and glossopharyngeal nerve while the posterior part transmits the vagus nerve, accessory and meningeal branches of the internal carotid artery. 7. Foramen magnum - Spinal roots of accessory nerves - It is the largest opening in the base of the skull. It serves as a junction area between medulla oblongata, spinal cord vertebral arteries and accessory nerves. It also serves as an attachment site for the dura mater, which is the outermost layer of the meninges. 8. Hypoglossal canal - hypoglossal nerve - It serves as the 12th passageway of cranial nerve. It is located between the condylar canal and the jugular foramen. Damage in this side can lead to damage in the hypoglossal nerve. Difficulty with speech, swallowing, and chewing. The tongue may also deviate to the affected side when protruded. 9. Carotid canal - Internal carotid artery - nerve plexus - it is a bony canal located in the petrous part of the temporal bone in the skull. It serves as a passageway for the internal carotid artery, a major artery that supplies blood to the brain. The carotid canal  is located on the anterior side of the petrous part of the temporal bone. It is medial to the jugular foramen and lateral to the foramen lacerum. 10. Foramen spinosum - Meningeal branch of mandibular nerve - It is a small opening in the lateral part of the greater wing of the sphenoid bone in the skull. It serves as a passageway for the middle meningeal artery and the middle meningeal vein. The foramen spinosum is located just posterior to the foramen ovale. 11. Foramen lacerum - it serves as the opening of the vagus nerve and glossopharyngeal nerve. It serves as the attachment site for the stylohyoid ligament. 12. - Not Available 13. Cribriform plate of ethmoid bone - Olfactory nerve - is a thin bony plate located in the roof of the nasal cavity. It is part of the ethmoid bone and separates the nasal cavity from the anterior cranial fossa. It is perforated with numerous small holes called foramina. This foramina allows the passageway of the olfactory nerve filament. This plate is surrounded by the lateral masses of the ethmoid bone, which contain the ethmoid air cells. Functional Areas and Nuclei 1. The oculomotor nucleus is located at the periaqueductal gray matter around the cerebral aqueduct. This nuclei is responsible in controlling the extraocular muscles which is the muscle that control the eye movement, it also plays a role in pupillary constriction and accommodation. Trochlear nerve is located in the midbrain, specifically the periaqueductal gray matter. It is situated at approximately the level of the inferior colliculi. It is responsible for controlling the superior oblique muscle. Abducens nerve nuclei are located in the pons, a part of the brainstem. They are situated near the midline, just lateral to the pontine nuclei. It is responsible for controlling the lateral rectus muscle, one of the six extraocular muscles that allow for the eye movement. 2. Nucleus in the picture: A: Green - Oculomotor nerve nucleus. B : Yellow: Edinger - Westphal nucleus 3. Trigeminal nerve is a cranial nerve with both sensory and motor function, it has three divisions namely the opthalmic, maxillary and mandibular division. The trigeminal motor nucleus is responsible for the control of the muscles of mastication, including masseter, temporais, pterygoid and medial pterygoid muscles. It is located in the pons, ventral to the trigeminal sensory nucleus. Trigeminal sensory nucleus is located in the pons, dorsal to the trigeminal motor nucleus. It receives sensory information from the face, scalp, and teeth. It is divided into three parts, the principal sensory nucleus, mesencephalic nucleus, and spinal nucleus. The trigeminal mesencephalic nucleus is located in the midbrain , rostral to the trigeminal sensory nucleus. It receives proprioceptive information from the muscles of mastication. It is only the sensory nucleus that extends into the brainstem. 4. Nuclei in the Medulla cross section. A: Medial vestibular nucleus B: Nucleus of tractus solitarius C: Nucleus of hypoglossal nerve D: Posterior nucleus of vagus nerve E: Spinal nucleus of trigeminal nerve F: Posterior accessory olivary nucleus 2. Special Sensory Functions: A. Vestibulocochlear nerve is a cranial; nerve that is responsible for hearing and balance. It is composed of two separate components; the cochlear nerve and the vestibular nerve. The cochlear nerve is responsible for hearing. It is composed of auditory nerve fibers that originate in the cochlea, a spiral shaped cavity in the inner ear. These fibers transmit sound vibration to the brain. The cochlear nerve enters the internal acoustic meatus and then travels to the brainstem, where it synapses with neurons in the cochlear nuclei. Vestibular nerve on the other hand is responsible for the balance. it is composed of vestibular nerve fibers that originate in the vestibular system, which is located in the inner ear. This system consists of three semicircular canals, the utricle, and the saccule, which are fluid filled structures that detect head movement and orientation. The vestibular nerve also enters the internal acoustic meatus and then travels to the brainstem, where it is synapse with neurons in the vestibular nuclei. B. Glossopharyngeal nerve is both sensory and motor and innervates different parts of the person’s head and neck. Sensory: Posterior one third of the tongue responsible for the taste. Tonsil - receives sensory information from tonsil. Pharynx - receives sensory information from pharynx, posterior wall and epiglottis. Eustachian tube - receives sensory information from the eustachian tube, a canal that connects the middle ear to the nasopharynx. In terms of motor, stylopharyngeus muscle is muscle that helps to elevate the pharynx during swallowing. Parotid gland, a salivary gland that produces saliva. Vagus nerve is the longest of the cranial nerves and both sensory and motor nerves innervating head, neck, thorax and abdomen. In terms of sensory, it receives information from the pharynx, larynx, trachea, esophagus, heart, lungs, diaphragm, and abdomen. While in terms of motor, it controls the muscles of the pharynx responsible for the swallowing and speech, larynx for vocalization and respiration, trachea, esophagus, heart, lungs, diaphragm, and abdomen responsible for the digestion and their function. Imaging Correlation 1. The cranial nerves found in the cavernous sinus include oculomotor nerve, trochlear nerve, abducens nerve, ophthalmic nerve, maxillary nerve. Lesions in cavernous sinus signs and symptoms include oculomotor nerve palsy, trochlear nerve palsy, abducens nerve palsy, optic nerve compression. Other signs and symptoms include facial pain, numbness, headache, and horner’s syndrome. 2. Cranial nerves in the Cavernous sinus MRI A. Oculomotor nerve B. Abducens nerve C. Ophthalmic nerve D. Trochlear nerve  E. Maxillary nerve Clinical Correlation 1. These are facial paralysis which can be classified as complete paralysis, partial paralysis, and central facial paralysis and other symptoms such as loss of taste, hyperacusis, dry eye, and bell’s palsy. Central palsy is caused by a stroke or other brain injury that affects the upper motor neurons controlling facial muscle. it may include weakness or paralysis on the opposite side of the body, depending on the location of the brain injury. It primarily affects the lower part of the face resulting in weakness or paralysis of the muscles below the mouth. The upper part of the face is usually spread. However in peripheral nerve palsy, the damage is the facial nerve itself which controls the muscle of the face, this can be due to the inflammation, trauma, and other factors. It affects the entire side of the face, resulting in weakness or paralysis of all facial muscles. Other symptoms include loss of taste on the affected side of the tongue, dry eye, and hyperacusis or increased sensitivity to sound. 2. Lesion in the hypoglossal nerve will lead to difficulty in tongue protrusion, impaired articulation, problems in swallowing, and difficulty in chewing. Clinical tests needed to assess its condition include tongue protrusion, tongue movement, tongue strength, speech evaluation, swallowing assessment, electromyography, nerve conduction studies. 2. Cranial Nerve Dysfunction 1. There will be ptosis or drooping of eyelid which is the first symptom to appear, diplopia or the double vision whereas the affected eye appears to be displaced laterally, limited eye movement in which the affected eye may be unable to adduct, elevate or depress, dilated pupil, and loss of accommodation or difficulty in focusing on near object. The common causes of this include compression, ischemia, inflammation and trauma. 2. When it is damaged, its effect would be massive, respiratory system (dyspnea, hoarseness, stridor, coughing), cardiovascular system (tachycardia, arrhythmias, vasodilation, hypotension), and gastrointestinal system (Dysphagia, nausea and vomiting, abdominal distension and decreased gastric motility) will be affected. Other effects include horner’s syndrome,loss of taste, urinary incontinence. It is diagnosed using medical history, physical exams like swallowing, speech, and reflexes. Imaging studies like CT scan or MRI, electrodiagnostic tests, and blood tests. Management includes medication such as anti inflammatory drugs, surgery, physical therapy, vagus nerve stimulation.